Various methods and the corresponding apparatuses are known in various embodiments—adapted to the bulk material to be treated—for impinging bulk material with accelerated electrons.
Thus an electron field having opposing velocity components of the electronics is generated in an evacuated chamber by opposing arrangement of two electron accelerators, through which electron field the bulk material is guided in free fall in an extended transparent stream (DD 291 702 A5). For the electron treatment, the bulk material is fed into the chamber via cellular wheel sluices and discharged again after the electron beam process. However, the disadvantage of such apparatuses is the high equipment expense for generating the electron field, since at least two electron accelerators are required, and the high expense of vacuum technology.
It is also known to generate an electron field having opposing velocity components such that the electron beam is diverted back to the particle stream by magnetic deflection after it has passed the bulk-material particles. Apparatuses of this type avoid the expense of a second electron accelerator. However, the disadvantage of this method consists in that, due to the relatively long path that the electron beam traverses in the process chamber, a substantially better vacuum is required, which requires an even greater equipment expense with respect to vacuum generation.
Methods and apparatuses are also known that work with two mutually opposing electron accelerators, wherein the electrons escape at atmospheric pressure via a beam-escape window (DE 44 34 767 C1). Here the bulk material is also guided in free fall through the electron field. In this solution the expense is omitted of the otherwise necessary evacuation of the process chamber. However, the disadvantage remains of the high equipment cost due to the required use of at least two electron accelerators.
It is furthermore known to impinge materials in powder form and materials in granular form with electrons at atmospheric pressure, wherein only one electron accelerator is sufficient for use and the to-be-irradiated particles are carried through the electron field in a gas stream (WO 98/43274 A1). The gas stream including the to-be-irradiated particles is guided through a rectangular channel, which is closed on one side with 25-μm-thick aluminum foil, through which the electrons penetrate after their discharge via a 13-μm-thick titanium window foil and pass the distance up to the radiating channel. Opposite the aluminum foil, the rectangular channel is formed by a flat plate made from a material of high atomic number. After penetrating the channel cross-section the electrons are backscattered from this plate to a certain component. The backscattered electrons have a velocity component opposing the original input direction of the electrons and make possible that the side of the particles facing away from original input direction of the electrons is also subjected to electron bombardment.
It is disadvantageous that the intensity of the irradiation by the backscattered electrons is significantly lower than the intensity of the irradiation by the electrons escaping directly from the beam escape window, which leads to an uneven irradiating of the individual particles. It is also disadvantageous that the gas velocity required for carrying the particles strongly increases with an increasing ratio of mass to the surface of the transported particles. Thus for large-grain bulk material—such as, e.g., wheat or corn—very high gas-flow velocities are required. At these high velocities the energy doses, transferable in the electron field are limited to very small—for numerous applications substantially too small—values. A further disadvantage of this known solution consists in that after escaping from the electron accelerator the electrons still must additionally penetrate the aluminum foil closing the rectangular channel before they encounter the to-be-treated particles. The electrons thereby suffer an additional undesired energy loss.
Finally in DE 199 42 142 A1 a device is disclosed wherein bulk material is guided in multiple free falls past an electron beam device and impinged with accelerated electrons. Due to the multiple traversals, in conjunction with a simultaneous mixing of the bulk material, the probability with this embodiment is very high that the particles of the bulk material are impinged on all sides by accelerated electrons. However the multiple traversals requires a large amount of time in the performing of the treatment process.